Field of Use
The present disclosure relates generally to power amplifiers, and more specifically, to power amplifiers utilizing phase advancement to achieve a desired phase correction on one or more paths of the amplifier.
Description of the Related Art
Wireless communication systems often employ power amplifiers for increasing the power of a high frequency signal. In a wireless communication system, a power amplifier is usually the last amplifier in a transmission chain (i.e., the output stage). High gain, high linearity, stability, and a high level of efficiency—the ratio of radio frequency (RF) output power to direct current (DC) power—are characteristics of an ideal amplifier.
In general, a high frequency power amplifier operates at maximum power efficiency when the power amplifier transmits peak output power. However, power efficiency tends to worsen as output power decreases. Recently, Doherty power amplifier architectures have been the focus of attention not only for base stations, but also for mobile terminals because of the architecture's high power-added efficiency.
A Doherty power amplifier includes two or more amplifiers, such as a carrier amplifier and a peaking amplifier. These amplifiers can be connected in parallel with their outputs joined by an offset transmission line, which performs impedance transformation. The peaking amplifier delivers current as the carrier amplifier saturates, thereby reducing the impedance seen at the output of the carrier amplifier. Thus, the carrier amplifier delivers more current to the load while the carrier amplifier is saturated because of a “load-pulling” effect. Since the carrier amplifier remains close to saturation, a Doherty power amplifier is able to transmit peak output power so that the total efficiency of the system remains relatively high.